Modern electronic systems and particularly those using large scale integrated circuit technology require high efficiency, high current, and fast switching power supplies. At the same time, many applications for these electronic systems require that the power supplies be small and of low profile. Low profile packaging requires that as many components as possible be surface-mounted. Power supplies for such electronic systems invariably contain one or more inductors or transformers, which are often their physically largest components. Inductor and transformer size and shape, therefore, usually impose a constraint on reduction of the size and profile of a power supply. Conventional power supply inductors and transformers are large, bulky, and thus less than optimally compatible with surface mount technology and high density, low profile power supply packaging.
Previous attempts to reduce transformer and inductor coil profile, or height, have included the etching of copper windings directly onto a printed wiring board. However, because printed wiring board etchings are limited to material thicknesses of only 1 to 2 mils, these windings are very limited in current carrying capacity. Therefore, printed inductor and transformer windings have found very limited application, and are entirely unsuitable for modern, high current power supplies.
The high currents used in power supplies for modern, high density electronic systems also impose a reliability risk on power supply components. A particularly high risk resides in all integrated circuit or printed wiring board vias used to connect transformers or their internal windings to other components or to each other. A via is conventionally defined as a metal connection from a metallization layer to a conductive integrated circuit component or lower metal layer through an intervening layer of insulating material. Integrated circuit or printed wiring board vias are generally not capable of carrying high currents, and account for additional manufacturing costs.
Consequently, a need exists for small, low profile, high density, surface mounted inductor and transformer windings with a minimum number of internal and external connections through vias.